BERLIN (Reuters) - German police arrested a 29-year-old man they said was an active member of Islamic State who was plotting a truck attack on an ice rink.

The arrest, a year after Anis Amri, a failed Tunisian asylum seeker with Islamist links, hijacked a truck and drove it into a Christmas market in Berlin, killing 12 people, comes as security services have warned of growing numbers of radical Islamists in Germany.

“He was considering an attack on the ice rink on the Schlossplatz in Karlsruhe,” police in the south-western state of Baden-Wuerttemberg said, adding that the suspect was a German citizen whose name they gave only as Dasbar W.

“To that end he was assessing areas around Karlsruhe Castle and, from September 2017, had begun seeking employment as a delivery driver - without success,” the police statement said.

In 2015, the suspect traveled to Iraq to fight for Islamic State, receiving weapons training and working as a scout seeking potential attack targets in the city of Erbil, police said. He returned to Germany the following year.

Before leaving for Iraq, Dasbar worked for Islamic State from Germany, producing propaganda videos and proselytizing to converts in online chat rooms, police said.

Earlier this month, Germany’s security service warned that the number of Salafists - followers of a radical Islamist ideology - had risen to an all-time high of 10,800, though the number prepared to mount attacks was in the order of hundreds.